diff --git a/src/vim9execute.c b/src/vim9execute.c
index fe78e8f..a49f3d7 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -2317,6 +2317,7 @@
 		    // slice: composite is at stack-3, indexes at stack-2 and
 		    // stack-1
 		    tv = is_slice ? STACK_TV_BOT(-3) : STACK_TV_BOT(-2);
+		    SOURCING_LNUM = iptr->isn_lnum;
 		    if (check_can_index(tv, TRUE, TRUE) == FAIL)
 			goto on_error;
 		    var1 = is_slice ? STACK_TV_BOT(-2) : STACK_TV_BOT(-1);
@@ -2463,6 +2464,7 @@
 		    int		error = FALSE;
 
 		    tv = STACK_TV_BOT(-1);
+		    SOURCING_LNUM = iptr->isn_lnum;
 		    if (check_not_string(tv) == FAIL)
 			goto on_error;
 		    (void)tv_get_number_chk(tv, &error);